Method for producing cyclopentadiene compounds

ABSTRACT

The invention relates to a method for producing substituted cyclopentadiene compounds and to cyclopentadiene compounds obtained by said method.

[0001] The present invention relates to a process for preparingsubstituted cyclopentadiene compounds.

[0002] Various methods of preparing substituted cyclopentadienecompounds are known. Many substituted cyclopentadiene compounds areprepared by addition of metal alkyls onto a cyclopenten-1-one or1-indanone derivative. A secondary reaction which frequently occurs isdeprotonation of the cyclopenten-1-ones and 1-indanones, which leads todimeric condensation products. These condensation products then have tobe separated off in a purification step. The purified addition productis then usually dehydrated to form the desired cyclopentadiene.Depending on the addition product, the dehydration requires conditionsunder which the substituted cyclopentadiene formed dimerizes and thenhas to be cracked again in a subsequent step. This synthesis iscomplicated and often leads to only low yields of the substitutedcyclopentadiene compounds.

[0003] In the case of very bulky substituents which are lessnucleophilic and more basic, the deprotonation of the cyclopenten-1-onesand 1-indanones occurs preferentially. Thus, cyclopentadiene compoundshaving bulky substituents are prepared using dilithioferrocene compoundsonto which electrophiles are added. However, this generally leads to1,1′- and 1-substituted ferrocenes. The cyclopentadiene compounds canthen be split off directly, for example by means of elemental lithium,to form lithium cyclopentadienyl compounds which can, for example, beused directly in the synthesis of metallocenes. However, as a result ofthe incomplete reaction with the electrophiles, the unsubstitutedstarting cyclopentadiene is also obtained, so that purification isgenerally also carried out here.

[0004] It is an object of the present invention to find a new processfor preparing substituted cycldpentadiene compounds which is simple tocarry out, leads selectively to the substituted cyclopentadienylcompounds and, in particular, is also suitable for the introduction ofbulky radicals.

[0005] We have found that this object is achieved by a process forpreparing substituted cyclopentadiene compounds, which comprises thefollowing steps:

[0006] (A) reacting a compound of the formula I

[0007] where the substituents have the following meanings:

[0008] M¹ is Co, Rh or Ir,

[0009] X is fluorine, chlorine, bromine, iodine, trifluorosulfonyl,tosyl,

[0010] Y are identical or different and each have the formula II

[0011] where the variables have the following meanings:

[0012] E¹-E⁵ are each carbon or at most one E¹ to E⁵ is phosphorus,

[0013] R¹-R⁵ are each, independently of one another, hydrogen,C₂-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₆-C₂₀-aryl, alkylaryl having from 1 to 10carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part,trialkylsilyl having three independent C₁-C₂₀-alkyl groups, where theorganic radicals R¹-R⁵ may also be substituted by halogens and/ornitrogen-, phosphorus-, sulfur- or oxygen-containing groups and twogeminal or vicinal radicals R¹-R⁵ may also be joined to form a five- orsix-membered ring,

[0014] with a compound M²X_(n)R6_(n-z),

[0015] where the variables have the following meanings:

[0016] R⁶ is C₁-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₆-C₂₀-aryl, alkylaryl havingfrom 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in thearyl part, trialkylsilyl having three independent C₁-C₂₀-alkyl groups oran unsubstituted, substituted or fused, partially unsaturatedheterocyclic or heteroaromatic ring system, where the organic radical R⁶may also be substituted by halogens and/or sulfur-, phosphorus-,nitrogen- or oxygen-containing groups,

[0017] M² is Li, Na, K, Mg, Al, B,

[0018] n is 0, 1 or 2 and is less than z,

[0019] z is an integer corresponding to the oxidation state of M²,

[0020] and

[0021] (B) reacting the intermediate obtained in this way with iron(III)chloride.

[0022] The cyclopentadienyl ring Y in Y₂—M¹ can also be aheterocyclopentadienyl ligand, i.e. a ring in which at least one carbonatom may be replaced by a heteroatom of group 15 or 16. In this case,preference is given to a C₅-ring carbon being replaced by phosphorus. Itis preferred that all atoms E¹-E⁵ are carbon.

[0023] Examples of possible organic radicals R¹-R⁶ are: C₁-C₂₀-alkylwhich may be linear or branched, e.g. methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl,n-octyl, n-nonyl, n-decyl or n-dodecyl, 5- to 7-membered cycloalkylwhich may in turn bear a C₆-C₁₀-aryl group as substituent, e.g.cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane,cyclooctane, cyclononane or cyclododecane, C₂-C₂₀-alkenyl which may belinear, cyclic or branched and in which the double bond may be internalor terminal, e.g. vinyl, 1-allyl, 2-allyl, 3-allyl, butenyl, pentenyl,hexenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl or cyclooctadienyl,C₆-C₂₀-aryl which may bear further alkyl groups as substituents, e.g.phenyl, naphthyl, biphenyl, anthranyl, o-, m-, p-methylphenyl, 2,3-,2,4-, 2,5- or 2,6-dimethylphenyl, 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6-or 3,4,5-trimethylphenyl, or arylalkyl which may bear further alkylgroups as substituents, e.g. benzyl, o-, m, p-methylbenzyl, 1- or2-ethylphenyl. In the trialkylsilyl radicals, suitable alkyl radicalsare, independently of one another, the same C₁-C₂₀-alkyl groups whichhave been described in detail above for R¹-R⁶, where two alkyl radicalsmay also be joined to form a 5- or 6-membered ring; examples of suchtrialkylsilyl radicals are trimethylsilyl, triethylsilyl,butyldimethylsilyl or tributylsilyl. The organic radicals R¹-R⁶ may alsobe substituted by halogens such as fluorine, chlorine, bromine or iodineand/or nitrogen-, phosphorus-, sulfur- or oxygen-containing groups suchas ═NR, —NR₂, ═PR, PR₂, —SR, ═S, —OR or ═O, where R is C₁-C₂₀-alkyl,C₂-C₂₀-alkenyl, C₆-C₂₀-aryl, alkylaryl having from 1 to 10 carbon atomsin the alkyl part and 6-20 carbon atoms in the aryl part ortrialkylsilyl having three independent C₁-C₂₀-alkyl groups as describedin detail for R¹-R⁶.

[0024] Two geminal or vicinal radicals R¹-R⁵ may also be joined to forma five- or six-membered ring, e.g. tetrahydroindenyl, indenyl,benzindenyl or fluorenyl, and the five- or six-membered rings can alsobe heteroaromatic, e.g. 7-cyclopentathiophene, 7-cyclopentadipyrrole,7-cyclopentadiphosphole, thiapentalene, 2-methylthiapentalene,azapentalene, oxapentalene, borapentalene or phosphapentalene.

[0025] Preferred radicals R¹-R⁵ are hydrogen, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl,n-octyl, vinyl, allyl, benzyl, phenyl, naphthyl, biphenyl and anthranyl.Particular examples of organosilicon substituents are trialkylsilylgroups having from 1 to 10 carbon atoms in the alkyl radical, inparticular trimethylsilyl groups. Some of the cyclopentadienyl systemsused for this purpose are commercially available.

[0026] To be able to utilize the substituted cyclopentadiene compoundsfor the synthesis of metallocenes, it is often customary to deprotonatethem by means of a strong base and to react the cyclopentadienyl anionobtained in this way with, for example, a transition metal halide. Whenusing this method, it is advantageous for at least one of R¹-R⁵ to be ahydrogen atom.

[0027] This method is particularly advantageous for starting compoundshaving simple and cheap Y systems. Particularly preferred radicals R¹-R⁵are therefore hydrogen, methyl or two vicinal vinylic groups whichtogether form an aromatic six-membered ring system; in particular, R¹-R³are each hydrogen and R⁴ and R⁵ together form a fused-on aromatic ringsystem, so that Y is an indenyl group.

[0028] A particularly simple and inexpensive Y system is unsubstitutedcyclopentadienyl in which all radicals R¹-R⁵ are hydrogen, and this istherefore also particularly preferred.

[0029] The two groups Y can be identical or different. In the case ofdifferent groups Y, this is only appropriate if. R⁶ reactspreferentially with one of the groups Y with a selectivity of over 90%.Preference is given to the two groups Y being identical, in particularwith inexpensive and readily available groups Y.

[0030] X is preferably chlorine, bromine or iodine, in particulariodine.

[0031] In the process, the cationic Y₂—M¹ compounds are used.Particularly well-suited compounds are Y₂-Co compounds, in particularthose in which X is iodine. An example of a particularly useful compoundis bis(cyclopentadienyl)cobalt iodide.

[0032] R⁶ can also be an unsubstituted, substituted or fused,heterocyclic aromatic ring system in which the ring contains not onlycarbon atoms but also heteroatoms selected from the group consisting ofoxygen, sulfur, nitrogen and phosphorus. Examples of heteroaryl groupshaving a 5-membered ring in which from one to four nitrogen atoms orfrom one to three nitrogen atoms and/or a sulfur or oxygen atom can bepresent as ring atoms in addition to carbon are 2-furyl, 2-thienyl,2-pyrrolyl, 3-isoxazolyl, 5-isoxazolyl, 3-isothiazolyl, 5-isothiazolyl,1-pyrazolyl, 3-pyrazolyl, 5-pyrazolyl, 2-oxazolyl, 4-oxazolyl,5-oxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 2-imidazolyl,4-imidazolyl, 5-imidazolyl, 1,2,4-oxadiazol-3-yl, 1,2,5-oxadiazol-5-yl,1,3,4-oxadiazol-2-yl or 1,2,4-triazol-3-yl. Examples of heteorarylgroups having a 6-membered ring in which from one to four nitrogen atomsand/or a phosphorus atom can be present are 2-pyridinyl,2-phosphabenzenyl, 3-pyridazinyl, 2-pyrimidinyl, 4-pyrimidinyl,2-pyrazinyl, 1,3,5-triazin-2-yl and 1,2,4-triazin-3-yl,1,2,4-triazin-5-yl or 1,2,4-triazin-6-yl. The heteroaryl groups having5- and 6-membered rings can also be substituted by C₁-C₁₀-alkyl,C₆-C₁₀-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkylpart and 6-10 atoms in the aryl part, trialkylsilyl or halogens such asfluorine, chlorine or bromine or be fused with one or more aromatics orheteroaromatics. Examples of benzo-fused 5-membered heteroaryl groupsare 2-indolyl, 7-indolyl, 2-coumaronyl, 7-coumaronyl, 2-thionaphthenyl,7-thionaphthenyl, 3-indazolyl, 7-indazolyl, 2-benzimidazolyl or7-benzamidazolyl. Examples of benzo-fused 6-membered heteroaryl groupsare 2-quinolyl, 6-quinolyl, 3-cinnolyl, 8-cinnolyl, 1-phthalazyl,2-quinazolyl, 4-quinazolyl, 8-quinazolyl, 5-quinoxalyl, 4-acridyl,1-phenanthridyl or 1-phenazyl. Nomenclature and numbering of theheterocycles have been taken from L. Fieser and M. Fieser, Lehrbuch derorganischen Chemie, 3rd revised edition, Verlag Chemie, Weinheim 1957.

[0033] The process of the present invention gives very good yields evenin the case of bulky radicals R⁶. In a preferred embodiment, R⁶ isnaphthyl, biphenyl, anthranyl, o-, m-, p-methylphenyl, 2,3-, 2,4-, 2,5-or 2,6-dimethylphenyl, 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6- or3,4,5-trimethylphenyl, benzyl, o-, m-, p-methylbenzyl, 1- or2-ethylphenyl or an unsubstituted, substituted or fused, heteroaromaticring system. R⁶ is particularly preferably an unsubstituted orsubstituted 8-quinolyl radical.

[0034] Particularly well-suited compounds for addition onto Y arelithium compounds in which M² is Li. The lithium compounds of thepreferred and particularly preferred groups R⁶ are very particularlyuseful.

[0035] The reaction A) can be carried out at from −100 to 50° C. Thereaction is preferably carried out at from −90 to 20° C., in particularfrom −90 to −50° C. Suitable solvents are aprotic solvents in whichM²X_(n)R⁶ _(n-z) is readily soluble. Examples of suitable solvents areethers such as diethyl ether, dibutyl ether, tetrahydrofuran, glyme ordiglyme, aromatic hydrocarbons such as toluene or xylene or hydrocarbonssuch as pentane, hexane, heptane or octane, and mixtures of the varioussolvents. Particularly well-suited solvents are tetrahydrofuran, andmixtures of tetrahydrofuran and hexane.

[0036] Y₂M¹X is reacted with M²X_(n)R⁶ _(n-z) in a molar ratio of Y(molar equivalents, based on total Y regardless of whether these areidentical or different) to R⁶ of from 1:0.1 to 1:5, preferably from1:0.4 to 1:1, particularly preferably from 1:0.45 to 1:0.55.

[0037] The reaction B) can be carried out at from −100 to 50° C. Thereaction is preferably carried out at from −90 to 20° C., in particularfrom −80 to −50° C. Suitable solvents are aprotic solvents in whichM²X_(n)R⁶ _(n-z) is readily soluble. Examples of suitable solvents areethers such as diethyl ether, dibutyl ether, tetrahydrofuran, glyme ordiglyme, aromatic hydrocarbons such as toluene or xylene or hydrocarbonssuch as pentane, hexane, heptane or octane, and mixtures of the varioussolvents. Particularly well-suited solvents are tetrahydrofuran andmixtures of tetrahydrofuran and toluene.

[0038] The intermediate from A) is reacted with iron(III) chloride,preferably anhydrous iron(III) chloride, in a molar ratio of Fe to M¹used in A) of from 1:0.5 to 1:5, preferably from 1:1 to 1:5,particularly preferably from 1:2 to 1:3.

[0039] The process of the present invention makes it possible to preparesubstituted cyclopentadiene compounds cleanly and in good yields. Thesecan subsequently be used for the synthesis of metallocenes. Inparticular, substituted cyclopentadiene systems which tend to dimerizecan be set free at low temperatures by the iron(III) chloride andreacted further, for example deprotonated, at these temperatures.Preferred cyclopentadienyl systems are, for example,1-(8-quinolyl)cyclopentadiene, 1-(1-naphthyl)cyclopentadiene and1-(2-methyl-8-quinolyl)cyclopentadiene.

[0040] The following examples illustrate the invention:

[0041] All work was, unless indicated otherwise, carried out in theabsence of air and moisture. Toluene and THF were dried over a column ofmolecular sieves or over sodium/benzophenone and distilled.

[0042] The following starting compounds were prepared by the literaturemethods cited:

[0043] 8-bromoquinoline

[0044] a) J. Mirek, Roczniki Chem. 1960, 34, 1599-1606.

[0045] Analysis

[0046] NMR samples were placed in the tube under inert gas and, ifappropriate, melted. The solvent signals served as internal standard inthe ¹H- and ¹³C-NMR spectra and the chemical shifts were converted intochemical shifts relative to TMS. NMR measurements were carried out on aBruker AC 200 and, in particular COSY experiments, on a Bruker AC 300.

[0047] Mass spectra were measured on a VG Micromass 7070 H and aFinnigan MAT 8230. High-resolution mass spectra were measured on JeolJMS-700 and VG ZAB 2F instruments.

Example 1 Preparation of 8-quinolylcyclopentadiene

[0048] 6.63 g of 8-bromoquinoline (31.8 mmol) were dissolved in 100 mlof THF in a 250 ml Schlenk flask and, at −90° C., 12.8 ml ofn-butyllithium solution (32 mmol, 2.5 M in hexane) were added dropwise.After stirring for 15 minutes, the dark reaction solution was addeddropwise by means of a transfer syringe to a suspension of 10 g ofcobalticinium iodide (31.6 mmol) in 200 ml of THF at −90° C. The redsolution formed was allowed to warm to room temperature overnight andsubsequently admixed with a little aluminum oxide (neutral) and thesolvent was removed under reduced pressure. The crude product wassubsequently chromatographed on a column of aluminum oxide (neutral)using toluene as eluant. Distilling off the solvent gave 8.15 g of(quinolylcyclopentadiene)(η5-cyclopentadienyl)cobalt(I) (25.7 mmol, 81%)as a red solid.

[0049] 1H-NMR (CDCl₃, 200 MHz): δ=3.16 (pq, Cp-CH); 4.87-4.93 (m, 6HC5H5 and quinoline-Cp-CH); (pt, 2H, Cp-CH); 5.29 (pt, 2H, cp-CH);7.06-7.12 (m, 1H, H⁷); 7.30-7.40 (m, 2H, H³ and H⁶); 7.54 (dd, ³J (H⁵,H⁶)=8.1 Hz, ⁴J (H⁵, H⁷)=1.5 Hz, 1H, H⁵); 8.04 (dd, ³J (H⁴, H³)=8.3 Hz,⁴J (H⁴, H²)=1.9 Hz, 1H, H⁴); 8.94 (dd, ³J (H², H³)=4.2 Hz, ⁴J (H²,H⁴)=1.8 Hz, 1H, H²).

[0050] EI-MS: m/e (%)=317 (M+, 10); 251 (M+-CpH, 100).

[0051] In a Schlenk flask, 2.05 g of(η4-8-quinolylcyclopentadiene)(η5-cyclopentadienyl)cobalt(I) (6.46 mmol)were dissolved in a mixture of 50 ml of toluene and 50 ml of THF andcooled to −78° C. A solution of 2.57 g of anhydrous iron(III) chloride(15.8 mmol) in 80 ml of THF at the same temperature was added dropwiseby means of a transfer syringe. The reaction mixture obtained wasstirred at this temperature for 1 hour and subsequently filtered at −30°C. through aluminum oxide (neutral) (30 cm, ø 2 cm, toluene) into a 500ml Schlenk flask which had been cooled to −78° C. The8-quinolylcyclopentadiene obtained in this way can be converted into thecorresponding aromatic, for example by means of sodium hydride, withoutfurther work-up. After taking off the solvent, 8-quinolylcyclopentadienewas isolated in a quantitative yield.

We claim:
 1. A process for preparing substituted cyclopentadienecompounds, which comprises the following steps: (A) reacting a compoundof the formula I

where the substituents have the following meanings: M¹ is Co, Rh or Ir,X is fluorine, chlorine, bromine, iodine, trifluorosulfonyl, tosyl, Yare identical or different and each have the formula II

where the variables have the following meanings: E¹-E⁵ are each carbonor at most one E¹ to E⁵ is phosphorus, R¹-R⁵ are each, independently ofone another, hydrogen, C₂-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₆-C₂₀-aryl,alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20carbon atoms in the aryl part, trialkylsilyl having three independentC₁-C₂₀-alkyl groups, where the organic radicals R¹-R⁵ may also besubstituted by halogens and/or nitrogen-, phosphorus-, sulfur- oroxygen-containing groups and two geminal or vicinal radicals R¹-R⁵ mayalso be joined to form a five- or six-membered ring, with a compoundM²X_(n)R⁶ _(n-z), where the variables have the following meanings: R⁶ isC₁-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₆-C₂₀-aryl, alkylaryl having from 1 to 10to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the arylpart, trialkylsilyl having three independent C₁-C₂₀-alkyl groups or anunsubstituted, substituted or fused, partially unsaturated heterocyclicor heteroaromatic ring system, where the organic radical R⁶ may also besubstituted by halogens and/or sulfur-, phosphorus, nitrogen- oroxygen-containing groups, M² is Li, Na, K, Mg, Al, B, n is 0, 1 or 2 andis less than z, z is an integer corresponding to the oxidation state ofM², and (B) reacting the intermediate obtained in this way withiron(III) chloride.
 2. A process for preparing substitutedcyclopentadiene compounds as claimed in claim 1, wherein M¹ is Co.
 3. Aprocess for preparing substituted cyclopentadiene compounds as claimedin claim 1 or 2, wherein the two groups Y are identical.
 4. A processfor preparing substituted cyclopentadiene compounds as claimed in any ofclaims 1 to 3, wherein at least one radical R¹-R⁵ is hydrogen.
 5. Aprocess for preparing substituted cyclopentadiene compounds as claimedin any of claims 1 to 4, wherein all the radicals R¹-R⁵ are hydrogen. 6.A process for preparing substituted cyclopentadiene compounds as claimedin any of claims 1 to 4, wherein R¹-R³ are each hydrogen and R⁴ and R⁵together form a fused-on aromatic ring system.
 7. A process forpreparing substituted cyclopentadiene compounds as claimed in any ofclaims 1 to 6, wherein M² is Li.
 8. A process for preparing substitutedcyclopentadiene compounds as claimed in any of claims 1 to 7, wherein R⁶is an unsubstituted, substituted or fused, heteroaromatic ring system.9. A process for preparing substituted cyclopentadiene compounds asclaimed in any of claims 1 to 7, wherein R⁶ is an unsubstituted orsubstituted 8-quinolyl system.
 10. A cyclopentadiene compound which canbe prepared by a process as claimed in any of claims 8 or 9.